In what situations is a double block and bleed system recommended?

A double block and bleed system is essential when isolating hazardous fluids and ensuring safety during maintenance. This system involves two valves with a bleed valve in between, providing a secure method to isolate potentially harmful substances. In the event of a failure in one of the valves, the second acts as a safeguard, preventing the ingress of hazardous fluids into areas where workers may be present. This enhanced safety feature is crucial during maintenance activities, as it minimizes the risk of exposure to harmful chemicals, vapors, or pressurized liquids, thereby ensuring a safer working environment.

In contrast, isolating non-hazardous fluids does not typically require the same level of safety precautions, making a double block and bleed system unnecessary in those scenarios. Structural inspections focus on the integrity of physical structures rather than fluid isolation, and monitoring system performance does not involve isolating fluids at all. Thus, the focus on safety for maintenance tasks related to hazardous fluids makes the recommendation for a double block and bleed system appropriate in this context.